1. Field of the Invention
This invention relates to a hand-held device for scanning two-dimensional bar code symbols and the like.
2. Description of Related Art
Bar codes have become broadly accepted as a means for automatically identifying objects. A bar code symbol is a pattern of parallel bars and spaces of various widths that represent data elements or characters. The bars represent strings of binary ones and the spaces represent strings of binary zeros. Generally, the bars and spaces can be no smaller than a specified minimum width which is called a "module" or "unit." The bars and spaces are multiples of this module size or minimum width.
The conventional bar code symbol is "one-dimensional" in that the bars and spaces extend only in a single direction. There has been an increasing need, however, for machinereadable symbols that contain more information than conventional bar code symbols. One approach for increasing the information in machine-readable symbols is to reduce the height of the bar codes and stack the bar codes one on top of each other to create a "stacked" or "two-dimensional" bar code. One such two-dimensional bar code is PDF417, which was developed by Symbol Technologies, Inc. The PDF417 symbology utilizes a variable number of codewords which are discrete representations of data. A complete description of the PDF417 code is contained in U.S. Pat. No. 5,304,786, which is assigned to the same assignee as the present invention and which is incorporated by reference herein. Other two dimensional bar code symbologies include Code 1 and Maxicode, which are referred to as matrix codes.
Both one-dimensional and two-dimensional bar code symbols are typically read by optical scanning techniques, such as by mechanically scanned laser beams or by self-scanning charge-coupled devices (CCD's), and the resulting electrical signals are then digitized and decoded to recover the data encoded in the symbol. In particular, two-dimensional bar code symbols such as those in PDF417 symbology may be scanned, either a stationary two-dimensional CCD array or by a linear (one-dimensional) CCD array. When a two-dimensional CCD array (e.g. 512 elements by 512 elements) is used, the array is stationary with respect to the symbol since it can capture the entire surface area of the symbol with one exposure; the stored charge relating to the amount of light reflected from the symbol is shifted out of the CCD array in serial format on a line-by-line basis in accordance with techniques well known in the art.
In order to scan a two-dimensional bar code symbol with a reader utilizing a linear or one-dimensional CCD array, the two-dimensional symbol and the linear CCD array must be put into motion relative to each other. That is, since a linear CCD array is capable of scanning in only one direction, it will only scan across the two-dimensional symbol. By physically moving or "swiping" the reader down the symbol (or vice-verse), the linear CCD array will scan each successive line of the two-dimensional symbol such that the entire symbol will be imaged. The image data can then be digitized and decoded in accordance with means known in the art. A twodimensional bar code reader which utilizes a linear CCD array to operate in this fashion is the PDF120 CCD Scanner marketed by the assignee of the present invention. The PDF120 CCD Scanner has digitizing circuitry and decoding software algorithms contained within the unit and outputs decoded PDF417 data to an RS-232 serial data port.
Other types of hand-held CCD scanning devices well known in the art include optical page scanners, which interface with a computer via a serial data port. Page scanners are used to scan text for input into an optical character recognition (OCR) software algorithm so that a user may scan a text document and have the computer convert the scanned image into text for use with a word processing program or similar application. Page scanners are also usefuil in capturing and storing a purely graphic image. Typically, page scanners require the user to manually adjust the contrast level of the scanner by means of trial and error.
Both the swipe-type PDF417 reader and the page scanning devices of the prior art have disadvantages, in particular when the reading device is used in conjunction with a personal computer in a desktop or so-called "office automation" environment. Both types of readers present large "footprints", i.e. they require a large mount of desk space. This is not only disadvantageous when the device is not in use, but it is also cumbersome when the device is used for scanning. In addition, both types of reading devices require the user to drag the device across the target symbol; thus, prior to scanning, the scanner physically covers the symbol and the user cannot see the symbol prior to initiating scanning. Since alignment of the reader with the symbol is critical. the inability to see the symbol for proper all,iiment is highly undesirable.
In addition, optical scanning devices in the prior art utilize a folded optical path from the viewing area to the CCD array sensor. The typical optical scanner is configured in a wand-type housing, with a handle that is held in the palm of the user's hand attached to a head which is swiped over the target symbol. Typically, a mirror or mirrors are used to reflect the image from the viewing area towards the CCD sensor. The use of mirrors introduce optical losses in the optical path due to various factors known in the prior art, and are thus disadvantageous.
It is therefore an object of the present invention to provide a hand-held two-dimensional bar code symbol reading device which overcomes these and other disadvantages of the prior art.
It is a further object of the present invention to provide such a hand-held two-dimensional bar code symbol reading device which allows the user to easily see the bar code symbol while aligning the reading device prior to scanning.
It is a further object of the present invention to provide such a hand-held two-dimensional bar code symbol reading device which leaves a small footprint on a user's desktop or other working area.
It is a farther object of the present invention to provide such a hand-held two-dimensional bar code symbol reading device which has a straight and mirrorless optical path from the viewing area to the CCD sensor array.